318 



NAME OF " GEYPHITE LIMESTONE.' 



[Ch. XXL 



these beds being separated by dark-colored narrow argillaceous partings, 

 so that the quarries of this ro(;k, at a distance, assume a, striped and 

 riband-like appearance.^ 



The Lias comprises, 1, the Upper Lias — thin limestone beds with clay 

 and shale ; 2, the Marlstone— a coarse shelly limestone ; and 3, the 

 Lower Lias — consisting of limestone, shells, and clay. These divisions 

 have certain fossils in common, and in some places pass the one into tli^ 

 other. 



Although the prevailing color of the limestone of this formation is 

 blue, yet some beds of the lower lias are of a ye'i.owish white color, and 

 have been called Avhite lias. In some parts of France, near the Vosges 

 mountains, and in Luxembourg, M. E. de Beaumont has shown that the 

 lias containing Gryphoea arcimia^ Plagiostoma giganteum (see fig. 400), 

 and other characteristic fossils, becomes arenaceous ; and around the Hartz, 

 in Westphalia and Bavaria, the inferior parts of the lias are sandy, and 

 sometimes afford a building-stone. 



The name of Gryphite limestone has sometimes been applied to the 

 lias, in consequence of the great number of shells which it contains of a 



Fig. 400, 



Fig. 401. 



Gryphma incurva, Sow. 



{G. arcuata, Lam.) 



Lias. 



Plagiostoma {Lima) giganteum. Sow. 

 Inf. Ool. and Lias. 



species of oyster, or Gryphcea (fig. 401 ; see, also, fig. 30, p. 29). A 

 large heavy shell called Hipyiwpodium (fig. 402), allied to Isocardia, is 

 also characteristic of the lower lias shales. The Lias formation is also 

 remarkable for being the oldest of the secondary rocks in which brachi- 

 opoda of the genera Spirifer and Leptoena (figs. 403, 404) occur : no 

 less than nine species of Sjnrifers are enumerated by Mr. Davidson as 

 belonging to the lias. These palliobranchiate mollusca predominate 

 greatly in strata older than the trias ; but, so far as we yet know, they 

 did not survive the liassic epoch. The marine beds of the lias also abound 

 in cephalopoda of the genera Belemnites^ Nautilus^ and Ammonites (see 

 figs. 405, 406, 407). 



Among the Crinoids or Stone-Lilies of the Lias, Pentacrinus Briareus 



Conyb. and Phil. p. 261. 



